I have also tried W7 on the R51 (of my Wife). Unfortunately there is no Drivers for W7. The R51 is too old. So I went back to XP.
The worst thing with W7 on R51 was lack of a dedicated Grafic Driver so the CPU was running at least 45% all the time.
I have put more RAM (now 1,5 GB) and a faster Hard Disk into the R51 which is now running very well with XP Pro.